CVE-2026-45063
HIGH
GHSA-ph86-p8f6-f9r2
Lifecycle Timeline
2DescriptionNVD
Description
X509Authenticator implements client-certificate (mTLS) authentication: the web server validates the client's certificate against a trusted CA, then passes the certificate's Subject DN (Distinguished Name: a string like CN=Alice,O=Example,emailAddress=alice@example.com) to Symfony via $_SERVER['SSL_CLIENT_S_DN']. Symfony extracts the user identifier from that string.
The extraction uses an unanchored regex that matches emailAddress= anywhere in the DN string: including inside the *value* of a different RDN (Relative Distinguished Name: one key=value component of the DN), such as CN. An attacker who can obtain a certificate from a trusted CA with a free-text CN can smuggle emailAddress=victim@target inside the CN value and be authenticated as the victim.
Resolution
The X509Authenticator now uses a regex that anchors the match to an RDN boundary (start of string, or following a , / / separator).
The patch for this issue is available here for branch 5.4.
Credits
Symfony would like to thank Claude Mythos Preview (via Project Glasswing) for reporting the issue and providing the fix.
AnalysisAI
Authentication bypass in Symfony's X509Authenticator (security-http component) lets an attacker who holds any certificate issued by a trusted CA impersonate another user during client-certificate (mTLS) authentication. Symfony extracts the login identifier from the certificate Subject DN using an unanchored regex, so an attacker can embed 'emailAddress=victim@target' inside a free-text CN value and be authenticated as that victim. …
Sign in for full analysis, threat intelligence, and remediation guidance.
RemediationAI
Within 24 hours: Inventory all Symfony deployments using X509Authenticator from the security-http component. Within 7 days: Apply the vendor-released patch across all maintained Symfony versions in production and staging environments. …
Sign in for detailed remediation steps.
Share
External POC / Exploit Code
Leaving vuln.today